1. Field of the Invention
This invention is in the field of medical instruments for processing body fluids including an instrument to perform hemodialysis.
2. Description of the Prior Art
The usual approach to performance of single access dialysis is to pump blood into the dialyzer by a roller pump on the arterial or inflow blood tubing. The venous limb has an air-filled tubing leading to a pressure gauge and a downstream clamp. The reading of the pressure gauge is the controller of the flow into the dialyzer, and the volume in the dialyzer. On inflow of blood to the dialyzer, the venous limb is clamped, the blood pump started, and the blood volume and pressure increase in the dialyzer and venous drip chamber. The relationship of pressure to the volume in the dialyzer is determined by the "compliance" or "stiffness" of the dialyzer. On outflow, the roller pump is stopped, and the venous clamp opened. The discharge of blood is entirely "passive." The volume in the dialyzer and drip chamber decrease. The degree of emptying of the dialyzer is indicated by the pressure fall at the venous drip chamber. The same relationship of pressure to volume in the dialyzer is dictated by the "compliance" curve for the dialyzer. The venous drip chamber itself acts as a significant "accumulator." In use of hollow fiber dialysis, the patient or nurse must watch to make sure that the air-blood lever in the drip chamber does not expand out of the chamber into the exiting tube and travel toward the patient. Alternatively, an ultrasound or optical monitor may be used to monitor the level of blood in the drip chamber. If an arterial drip chamber is used to monitor the pressure on the inflow tube to the dialyzer (to measure resistance or clotting of the dialyzer), the air-blood interface on the chamber must also be monitored. In short, the operation of a standard "single access" adapter to a dialysis system adds to the complexity of dialysis. Partly for this reason, single access dialysis is rarely used for home dialysis.
In the system disclosed herein, the blood volume in the dialyzer is also related to pressure in the dialyzer by the compliance curve. However, rather than measuring the fullness of the dialyzer by changes in pressure in the venous drip chamber, the system measures the rate flow into and out of the dialyzer directly.
A commercially available plate dialyzer is used (Cobe 1.6M2), with know compliance curves. Two optical flow meters are used, one on the inflow (arterial) blood tubing, and one on the outflow (venous) blood tubing. The optical sensors measure the flow of blood and abnormal particle content. As the dialyzer fills, the internal pressure increases and the rate of inflowing blood diminishes. The dialyzer empties passively. The rate of flow diminishes as the blood volume within the dialyzer diminishes. The degree of filling and emptying of the dialyzer and blood flow are optimized through flow monitoring as well as by the older method of measurement of the venous drip chamber pressure.
With PVC tubing, a standard roller pump has a maximal negative pressure (about -450 mm Hg) and a positive pressure achievable of over 1000 mm Hg. Thus, an arterial roller pump, such as used in the prior dialysis instruments, can exert a highly negative pressure on a fistula needle or catheter, in the case of blockage or venous collapse. Without an "arterial" drip chamber and pressure monitor, a clotted dialyzer in front of the pump can receive very high positive pressure. The system disclosed herein uses a roller pump on the outflow dialysate tube to expand dialyzer membranes and move blood into the dialyzer. Thus, the transmembrane pressure is substracted from the maximum negative pressure created by the roller pump, diminishing this pressure by 100-200 mm Hg. Furthermore, the maximal forward pressure cannot be delivered to the dialyzer, but only to the dialysis side components. In addition, the dialyzer membranes dampen some of the variations in flow providing a smoother flow of blood into the dialyzer.
In my U.S. Pat. Nos. 4,071,444 and 4,348,283 I have disclosed reciprocating dialyzers using a sorbent suspension. Another dialysis machine is available from Drake Willock under model number 8806/8805/8802 and is similar to the system disclosed herein in that single needle dialysis is performed by controlling the blood flow alternately into and out of a single needle veni-puncture; however, the Drake Willock model requires use of a venous drip chamber unlike my system and further utilizes a blood pump in lieu of a dialysate pump. Another commercially available dialysis machine is Organon Teknika Sorbsystem model SS-D which also utilizes a blood side pump with either a two needle access or single needle access. The number and quantity of disposables used with a dialysis instrument necessitates in the prior art devices considerable attention by the operator to insure proper usage. The system disclosed herein is provided with a removable cartridge which may be discarded containing all of the disposables needed for multiple dialysis treatments. The system utilizes a dialysate-side pumping mechanism for providing single needle dialysis. Thus, the system is more adaptable for use at home since the user may simply mount a fresh cartridge for dialysis, and remove and discard the cartridge at the end of each dialysis treatment.